I have assembled a huge collection of free wallpapers, most of them are great fro peeps that run Windows (XP to 7), but then there are many other free wallpapers like ones for android, for mobile phones, for iPhone, and more. You can download them all for free (you might get asked to complete a survey, depending on your location, but that takes like a minute).
Once you download them, simply unzip, and have fun.
Here are some of the free wallpapers that are in the file (way too many to post all of them here). Most of them are super awesome, some of them are not so decent, but you will have to sort them out and simply pick the ones that you like. I had to shrink the images to fit here, but most of the free wallpapers are in high resolution